In offshore installations, such as subsea production installations, there is an increasing use of electrically powered subsea equipment. Such subsea equipment may include, e.g., compressors, pumps, and any other electrically powered subsea equipment.
The electrical power to be distributed to such subsea equipment may be supplied from land, e.g. an onshore power plant, or from an offshore power generating facility, e.g. on a ship or platform.
Such subsea equipment may have high power requirements, and electric power must usually be transferred across long distances. In order to provide an efficient power transfer across long distances, a high voltage is used for the remote power supply.
The high voltage power supply is connected to subsea power distribution device which includes a transformer that provides a lower voltage power supply which is connected to subsea power consuming devices. The transformer may be accommodated in a watertight housing. The transformer may be a multi-winding transformer, having a primary winding and a plurality of secondary windings. The primary winding is electrically connected to input terminals which are arranged to be connected to the remote, high voltage power supply. The secondary windings are electrically connected to output terminals which are further arranged to be connected to the subsea power consuming devices.
A disadvantage of such an arrangement is that the secondary transformer windings have no protection against a failure in one of the circuits connected to a secondary winding, e.g. a ground fault, an overload or a short circuit in one of the subsea power consuming devices.
Such a failure may therefore result in the shutdown or disconnection of the entire transformer. This has substantial operational consequences, e.g. loss of operational time and costs, and should be avoided when possible.